This invention relates to a novel thread and bearing lubricant composition, and is particularly directed to a lubricant and sealant composition for downhole applications in the oil industry where high temperatures and forces are encountered.
Many oil filed tube and casing system, and many down-hole drilling tools and devices such as drill bits and roller reamers are required to operate in high pressure, high temperature environments that may be corrosive. Furthermore high loads and stresses are imposed on mating surfaces, so that in lubrication of contacting surfaces it becomes extremely difficult to provide a system that functions well under all these conditions.
A typical prior art lubricant composition for demanding (high pressure or high stress, or both) applications comprises a grease, powdered graphite, lead powder, zinc dust and copper flake. Such composition has been employed on stainless steel tube and casing systems needed for high temperature corrosive environments, but not satisfactorily because of certain problems with stainless steel, which is particularly subject to galling under these conditions.
Frequently there is severe galling of the contacting threads of stainless steel couplings and pipe threaded pin ends during make-up, and frequently also the contacting threads of the couplings seize on break-out. Gall stress in stainless steel arises from high point contact loading, resulting in localized heating that fluidizes or vaporizes the thread lubricant medium (e.g. grease) in the lubricant compound.
Other prior art lubricants for these applications include molybdenum di-sulfide, lithium based greases and teflon based pipe dopes. None have heretofore satisfactorily met the requirements imposed by high temperature, high stress loaded systems. Commonly, the low viscosity carrier for the lubricating solids has tended to bake-out or cook-out of the thread or bearing region at high temperature and pressure. Bake-out is caused principally by heat conduction into the region from a radiant or conducive source. Cook-out results from the intrusion of high temperature fluids into the threaded root helix, or the mating surfaces of bearing areas. In either event, only a dried residue of decomposition that is devoid of sealing capability is left. Moreover, the dried residue interposed between thread or bearing surfaces has such low lubricant properties that it generates extra friction, on breakout of a coupling for example, resulting in galling of the members.
It is desirable to provide a thread and bearing having enhanced lubrication and sealing properties, and which is resistant to breakdown under the high temperature and environmental conditions encountered in oil and gas well production pipes and especially geothermal applications. Further, such lubricant must conform to ASTM specifications for casing, tubing and line pipe thread compound. It is also desirable to provide an improved lubricant composition having the aforementioned advantageous properties, and formed of readily available constituents which can be easily formulated into a storable mix that can be applied with facility to thread or bearing surfaces at any location, such as a pipe mill, a pipe yard, a machine shop, and especially when running pipe into the well bore at the rig site.